As a conventional article monitoring apparatus to monitor movement of an article, for which payment has not been made, from a predetermined region, Japanese Published Examined Patent Application No. 2-43228 discloses an apparatus comprising an alarm device having a transmission antenna which transmits radiant energy within a predetermined region and a reception antenna which receives the radiant energy from the transmission antenna, and an article monitoring apparatus attached to an article to be monitored. When the article monitoring apparatus approaches the alarm device, the approach is detected, and the alarm device outputs an alarm.
Further, another article monitoring apparatus outputs an alarm by the apparatus itself when it is removed from an article.
Further, in another arrangement, a transmission antenna which transmits a predetermined electromagnetic wave or a radio wave of a predetermined frequency is set at, e.g., an entrance of shop floor, and when an article monitoring apparatus attached to an article detects the electromagnetic wave or radio wave from the transmission antenna, the article monitoring apparatus outputs an alarm.
However, in these apparatuses, occurrence of a false alarm is a serious problem. That is, an alarm is sounded even if no unpaid article has been taken out, or the attached apparatus has not been removed from the article. In such cases, an inappropriate reaction to customers will result in gross negligence.
Accordingly, in this type of system, it is necessary to precisely determine whether or not an alarm has been outputted because of a false alarm.